Time-delay fuse element

ABSTRACT

A time-delay fuse element comprises a core wire composed of at least two fusible electroconductive resistance wires wound together helically and a fusible electroconductive resistance member covering the core wire. At least one of the resistance wires forming the core wire is coated with a meltable electrically insulating material. The resistance wire covering the core wire has a lower electric resistance than the core wire.

United States Patent [1 1 Kasamatu TIME-DELAY FUSE ELEMENT [76] Inventor: Mikizo Kasamatu, 22-7,

Korikitano-cho, Neyagawa-Shi, Osaka, Japan [22] Filed: Dec. 19, 1973 211 Appl. No: 426,135

{30} Foreign Application Priority Data Dec. 26, 1972 Japan 48-931 [52] US. Cl 337/164, 337/296, 337/416 [51] Int. Cl. H0lh 85/12 158] Field of Search 337/164, 163, 166,293, 337/295, 290,296, 160, 283, 415, 414, 416, 417

[56] References Cited UNITED STATES PATENTS 1,068,341 7/1913 Hope 337/296 [4 1 Mar. 4, 1975 5/1927 Feldkamp 337/296 5 23/1950 Jackson 337/415 Primary Examiner-Harold Broome Attorney Agent, or Firm-Larson. Taylor & Hinds [57] ABSTRACT A time-delay fuse element comprises a core wire composed of at least two fusible electroconductive resistance wires wound together helically and a fusible electroconductive resistance member covering the core wire. At least one of the resistance wires forming the core wire is coated with a meltable electrically insulating material. The resistance wire covering the core wire has a lower electric resistance than the core wire.

8 Claims, 8 Drawing Figures TIME-DELAY FUSE ELEMENT The present invention relates to improvements in time-delay fuse elements.

Various fuse elements have heretofore been provided which have time-delay characteristics at excessive current. For example, a time-delay fuse element is known which comprises an electroconductive resistance wire of alloy predominantly consisting of manganese and nickel and coated with copper and another electroconductive resistance wire of tungsten helically wound around the alloy resistance wire. With this type of fuse element, the intended time-delay characteristics are given by the difference between the two wires in properties, i.e., chiefly in melting point, and the helical winding produces a high counter electromotive force where excessive current is present to add to the timedelay effect. However, the fuse element has the drawback that the kinds of materials usable for the electroconductive resistance wires are extremely limited, whilst the materials are expensive. The known fuse element is not applicable to a wide variety of uses therefore. Another type of time-delay fuse element is also known which is made of a copper plate or copper rod constricted at the desired portion, the constricted portion being covered with lead or lead alloy when so required. This type of fuse element is difficult to make because of its shape, entailing a further difficulty to assure satisfactory stable pre-arcing time/current characteristics.

A main object of this invention is to provide a timedelay fuse element which exhibits outstanding timedelay characteristics in the presence of excessive current such that it is fusible in at least three stages, the time-delay fuse element further having satisfactory prearcing time/current characteristics to give a time-delay effect that is adjusted as desired.

Another object of this invention is to provide a timedelay fuse element which is adapted to display satisfactory pre-arcing time/current characteristics at the desired amperage by varying the length and thickness of each component of the fuse element and which is applicable to cartridge fuses, screw-clamp type fuses, fuses having connecting sleeves or fuses of any type, the fuse element further being easy to make and inexpensive in respect of the materials used and suitable for mass production.

The time-delay fuse element according to this invention comprises at least two fusible electroconductive resistance wires, one of the resistance wires being coated with a meltable electrically insulating material, at least the coated resistance wire being helically wound around the other resistance wires, and a fusible electroconductive resistance member covering the core wire and having a lower electric resistance than the core wire.

Thus when abnormal excessive current flows through the time-delay fuse element of this invention incorporated in an electric circuit as upon energization of the circuit, the excessive current flows chiefly through the fusible conductive resistance member covering the core wire and lowest in electric resistance to fuse the resistance member at the midportion of the fuse element and the fused portion is removed from the core wire. Subsequently, the excessive current flows through the core wire, principally through the fusible electroconductive resistance wire which is not coated with the meltable electrically insulating material, heating the midportion of the bare wire to a high temperature, whereby part of the meltable electrically insulating coating on the other fusible electroconductive resistance wire in contact with the heated portion is fused and removed. As a result, the two fusible electroconductive resistance wires come into electrical connection with each other at the fused portion to substantially reduce the resistance and withstand the excessive current for a while. If the excessive current continues to flow thereafter, the fuse element will then be melted completely.

Thus the fuse element of this invention exhibits at least three stages of pre-arcing time/current characteristics at excessive current. Furthermore by varying the length and thickness of each component of the fuse element as desired, it is possible to obtain satisfactory prearcing time/current characteristics and therefore to adjust the time-delay characteristics with ease.

The fuse element of the present invention can be used for time-delay fuses of any type such as cartridge type fuses, screw-clamp type fuses, fuses having connecting sleeves and the like, are easy to make and can be manufactured in large quantities inexpensively inasmuch as there is no need to give strict consideration to the properties of material of the resistance wires to be used unlike conventional fuse elements of this type.

For a better understanding of this invention, the invention will be described below with reference to accompanying drawings showing preferred embodiments, wherein;

FIG. 1 is a front view showing a fuse having connecting sleeves and including a time-delay fuse element according to thisinvention;

FIG. 2 is an enlarged view showing the fuse element partly in section along its axial direction;

FIG. 3 is a view on a further enlarged scale showing the fuse element partly in section along the axial direction thereof;

FIG. 4 is an enlarged view in section taken along the line IV-IV in FIG. 1;

FIG. 5 is a view illustrating a covering member as it has been partly fused and removed;

FIG. 6 is a view illustrating a meltable electrically insulating material as it has been partly fused and removed;

FIG. 7 is an enlarged view showing another embodiment of fuse element of this invention partly in section along its axial direction; and

FIG. 8 is an enlarged view in cross section showing the fuse element of FIG. 7.

FIGS. 1 to 6 show a time-delay fuse element according to this invention which is designed for use in a lowvoltage household power supply circuit at current rating of 50 amp. The fuse element includes an electroconductive resistance wire 3 made of pure copper and wound around the resistance wire 1 closely and helically. The resistance wire 3 is coated with a meltable electrically insulating material 2 of polyurethane resin to a thickness of 0.025 mm and has a diameter of 0.4 mm. The resistance wires 1 and 3 form a core wire. The core wire is covered with an electroconductive resistance member 4 made of a lead alloy composed of percent lead and 10 percent tin and in the form of a tube measuring 3.4 mm in outer diameter and 1.52 mm in inner diameter. The time-delay fuse element is 22.5

Excessive current Melting time 67.5 amp 4 min. I amp 48 sec. 250 amp 6 sec.

FIGS. 7 and 8 show another embodiment of timedelay fuse element of this invention for a motor at a current rating of 22 amp. The fuse element includes an electroconductive resistance wire 11 0.44 mm in diameter and made of pure copper and another electroconductive resistance wire 13 of pure copper wire measuring 0.4 mm in diameter and coated with meltable electrically insulating materiallZ prepared from polyurethane resin to a thickness of 0.025 mm. The resistance wires 11 and 13 are twisted together at a pitch of 2.25 mm to wind each wire around the other in helical manner and to thereby form a core wire. The core wire is covered with a tubular electroconductive resistance member 14 made of pure lead and measuring 2.5 mm in outer diameter and 0.91 mm in inner diameter. The time-delay fuse thus constructed is 29 mm in length and is fixedly provided at its opposite ends with copper terminals of the screw-clamp type (not shown).

The time-delay fuse was used for a motor at a current rating of 22 amp with the following time-delay characteristics.

Although the core wire in each of the foregoing two embodiments is made of two fusible electroconductive resistance wires, the number of resistance wires may be increased to give improved time-delay characteristics. Further according to this invention it is not critical that the helical winding of the core wire extend over the entire length of the fuse element, but a required length of helical winding may be formed at an intermediate portion of the fuse element.

The present invention is not to be limited to the foregoing principal embodiments which are given for illustrative purposes only. Various other modifications and alterations which may be made by one skilled in the art are all to be included within the scope of this invention insofar as they do not depart from the appended claims.

What I claim is:

1. A time-delay fuse element comprising at least two fusible electroconductive resistance wires, one of .the resistance wires being coated with a meltable electrically insulating material, at least the coated resistance wire being helically wound around the other resistance wire to form a core wire constituted by the two resistance wires, and a fusible electroconductive resistance member covering the core wire and having a lower electric resistance than the core wire.

2. The time-delay fuse element as set forth in claim 1 wherein the resistance wires are twisted together so as to wind each of the wires around the other wire helically to form the core wire.

3. The time-delay fuse element as set forth in claim 1 wherein the resistance wires are made of pure copper.

4. The time-delay fuse element as set forth in claim 1 wherein polyurethane resin is used as the electrically insulating material coating the resistance wire.

5. The time-delay fuse element as set forth in claim 1 wherein the resistance member covering the core wire is made of lead.

6. The time-delay fuse element as set forth in claim 5 wherein the resistance member covering the core wire is in the form of a tube.

7. The time-delay fuse element as set forth in claim 1 wherein the resistance member covering the core wire is made of a lead alloy.

8. The time-delay fuse element as set forth in claim 7 wherein the resistance member covering the core is in the form of a tube. 

1. A time-delay fuse element comprising at least two fusible electroconductive resistance wires, one of the resistance wires being coated with a meltable electrically insulating material, at least the coated resistance wire being helically wound around the other resistance wire to form a core wire constituted by the two resistance wires, and a fusible electroconductive resistance member covering the core wire and having a lower electric resistance than the core wire.
 2. The time-delay fuse element as set forth in claim 1 wherein the resistance wires are twisted together so as to wind each of the wires around the other wire helically to form the core wire.
 3. The time-delay fuse element as set forth in claim 1 wherein the resistance wires are made of pure copper.
 4. The time-delay fuse element as set forth in claim 1 wherein polyurethane resin is used as the electrically insulating material coating the resistance wire.
 5. The time-delay fuse element as set forth in claim 1 wherein the resistance member covering the core wire is made of lead.
 6. The time-delay fuse element as set forth in claim 5 wherein the resistance member covering the core wire is in the form of a tube.
 7. The time-delay fuse element as set forth in claim 1 wherein the resistance member covering the core wire is made of a lead alloy.
 8. The time-delay fuse element as set forth in claim 7 wherein the resistance member covering the core is in the form of a tube. 